The discovery that a colossal solar flare hit Earth in the Dark Ages reminds
us that catastrophe could strike at any time, says Michael Hanlon

Considering the dangers lurking out there, it’s a wonder that our little planet is not in the firing line more often. We are just 93 million miles from a star that, while mostly well-behaved, occasionally has temper tantrums that could bring our civilisation to its knees. Our solar system is home to a swarm of comets, rocks, boulders and flying mountains, tens of thousands of which are big enough to wipe out anything from a small city to the entire biosphere. And further out lurk delinquent stars whose death explosions are the largest since the Big Bang. If one of these went off nearby, it would be curtains for all of us.

In fact, Earth can be considered rather lucky to have not suffered a total cataclysm in at least 3.5 billion years – the period during which we have an unbroken record of life existing on the Earth’s surface. Before then, global sterilisation events, caused by collisions with huge space rocks, almost certainly took place many times – perhaps once every few hundred years. Each may well have wiped out early versions of life. Then, after one final cataclysmic impact, it was plain sailing all the way.

That was what we used to think, anyway. But in recent decades, it has become clear that our cosmic neighbourhood, in more recent times, has not been as benign as was thought. In the 1980s, for example, it was confirmed that Earth has been hit several times in its history by objects from space – none big enough to sterilise the planet completely, but a handful packing enough of a punch to change the course of life forever. The most famous of these was our collision with a six-mile-wide asteroid 65 million years ago, whose fiery passage into the Mexican coast has been blamed for killing off, or at least delivering the coup de grâce to, the dinosaurs.

It is not just rocks we have to worry about. Japanese scientists have uncovered evidence from the study of tree rings that in the year 775 the Earth was hit by a colossal solar flare. The scientists found a spike in radioactive carbon-14, taken up by the ancient cedar trees they were studying. In Finland, Ilya Usoskin and his colleagues found an identical spike on the other side of the world. One theory is that this was caused by a nearby exploding star – a supernova – showering the Earth with radiation.

The trouble, says Usoskin, was that they could see no sign in the skies of a supernova remnant within the required distance. So the scientists turned to the historical record to see if there were any clues. The handful of supernovae that have burst into existence in historical times have often been well-recorded. But, 1,238 years ago, there were reports not of a brilliant “new star” but – as one English chronicler, Roger of Wendover, put it – of the skies themselves catching fire: “Fiery and fearful signs were seen in the heavens after sunset; and serpents appeared in Sussex, as if they were sprung out of the ground, to the astonishment of all.”

This was, says Usoskin, probably an account of an aurora borealis – the Northern Lights. “Anyone who has seen aurorae knows they look like serpents,” the Finnish scientist told New Scientist this week. The conclusion is that the Earth was hit by a huge mass of charged particles ejected from the Sun.

This was far from a one-off: such flares probably happen every few centuries or so. In late August and early September 1859, the Earth was hit by a smaller flare that had equally dramatic effects. Named the Carrington Event, after the astronomer who documented it fully, the solar storm caused Californian Gold Rush miners to be woken in their tents by the bright northern lights. Aurorae were seen as far north as Queensland in the southern hemisphere and as far south as Washington DC in the northern.

Nasa time-lapse video captures massive sun burst in May 2013

As with the storm of 750, the main impact on humans was a pretty light show on the ground: there is no evidence that solar storms of this intensity can damage or affect life directly. But there was also a chilling foretaste of what would happen if such an event were to repeat itself today. For the surge of charged particles had a dramatic impact on the nascent telegraph systems of the world. What author Tom Standage has called “the Victorian internet” was virtually knocked out. Telegraph wires were short-circuited, copper cables melted and some operators were given bad electrical shocks.

The world of 1859 was still one of steam and horse power, candle light and gas lamps. There was no domestic electricity, no telephones and no radio. If a rerun of the Carrington Event were to happen tomorrow, it would be cataclysmic: power lines would melt, electrical sub-stations would catch fire, half the world’s telephone grid would be knocked out, telecoms satellites would go down and the internet would be crippled, perhaps for a year. There would be massive disruptions to food and water supplies, water treatment and distribution, as well as the global banking system. All the finely tuned technological threads upon which our civilisation depends would be strained to breaking point.

Just repairing the power lines would take weeks – if an adequate supply of copper could be found. In June, a joint UK-American study, led by insurers Lloyd’s, estimated that a superstorm of this magnitude would cost the world £1.6 trillion, and tip the planet into depression.

Yet when it comes to such threats from space, we suffer from profound short-sightedness. Asteroid strikes, for example, are seen as the stuff of bad Hollywood films – or at least they were until February 15 this year, when the Russian city of Chelyabinsk was blasted by a 10,000-ton meteor that exploded at 30,000mph about 10 miles overhead. The blast, comparable to a small nuclear weapon, caused havoc on the ground, smashing windows and injuring more than 1,000 people, some seriously. A hundred and five years previously, Tunguska, also in Russia, was hit by an even bigger rock, or comet, that could have flattened Moscow (or London) if its trajectory had been only slightly different.

As well as being short-sighted, we are also ignorant. Solar storms in particular are poorly understood. Some are high-energy yet do little damage; other, more modest eruptions can cause chaos, such as the 1989 flare that knocked out the power grid in eastern Canada.

It is now thought that the biggest – such as the 775 event – may be the result of huge comets colliding with the Sun. According to David Eichler, an Israeli physicist at Ben Gurion University, a “sungrazer” comet 50 miles wide hitting the sun at a million miles an hour would generate enough energy to cause a solar flare that, if it hit the Earth, would be far more severe than even the Carrington Event.

There may be other weird things going on above our heads that we do not understand at all. Meteorologists have long thought that thunderstorms are caused by electrical charges building up in ice particles suspended in clouds. The trouble is, according to the Russian physicist Alexander Gurevich, that there simply isn’t enough energy to make the lightning flashes we see.

He proposes instead that these electrical discharges must be “seeded” in some way. His proposed mechanism involves cosmic rays – high-energy sub-atomic particles created by exploding stars and colliding black holes in distant galaxies – that cause a “runaway electron breakdown” by ionising the water in the atmosphere, generating immense electrical charges.

If he is right – and his is still a controversial theory – the next time you see a lightning strike, you may be witnessing something triggered by an exploding star or burping black hole millions of light years away. It is a reminder that, while we think of space as quiet, dark, silent and mostly harmless, that isn’t always the case.